1. Technical Field
The present invention generally relates to display technology fields and, particularly to a shift register.
2. Description of the Related Art
In the prior art, a shift register is proposed to be fabricated directly on a substrate for example a glass substrate, and a process for fabricating the shift register primarily is an amorphous silicon process. Since the amorphous silicon material has low carrier mobility, large size thin film transistors are necessarily needed to be designed for effectively driving scan lines of display panel. However, the large-sized thin film transistors inevitably occupy much more space of the display panel, and thus it is unsatisfactorily to be applied display panel products having narrow border or limited circuit region. Furthermore, large-sized thin film transistors would cause large parasitic capacitance effect, resulting in the increase of power consumption on clock pulse signal lines. In other words, the approach of fabricating the shift register directly on the substrate although can reduce the cost of gate driving circuit, if the size and power consumption issues associated with the thin film transistors would not be improved, the application of such approach inevitably is limited.
Accordingly, if a semiconductor material having high carrier mobility is attempted to be applied to the design of shift register, the size of the thin film transistor might be effectively minimized and the power consumption correspondingly can be decreased. Generally, the semiconductor material having high carrier mobility has larger switch-on current as well as switch-off current. Taking indium gallium zinc oxide (IGZO) as recently proposed as an example, a carrier mobility of IGZO is about 5 volts per meter-second (V/m·s), and a threshold voltage of the finally-completed thin film transistor is about −5 volts. Accordingly, if attempting to apply the IGZO semiconductor material to the shift register associated with the prior art, a large leakage current would be produced, which results in the shift register being unserviceable.